The cured product from the epoxy resin has many merits such as excellent dimensional stability, mechanical strength, electrical insulation, heat resistance, water resistance, chemical resistance and the like. However, the cured product obtained from the epoxy resin shows very brittle property due to small fracture toughness, so that this property has the influence on the applications of the wide range in some cases.
Patent Document 1 discloses a technology of improving the toughness and the impact resistance of the cured product obtained by dispersing polymer fine particles in the curable resin composition containing a curable resin such as an epoxy resin as main component.
Patent Document 2 discloses a technology for applying the epoxy resin having the toughness and the impact resistance to adhesive and the like. Various inorganic fillers are added to the epoxy resin for the purpose of the improving the workability such as dripping prevention or the purpose of controlling the physical properties of the cured product obtained.
Adhesive using the epoxy resin composition having the toughness and the impact resistance has been used in a structural adhesive for vehicle, and the strength of impact and peel-resistant adhesion to described in ISO 11343 has been regarded as important.
Patent Document 3 discloses a curable resin composition containing a curable resin and a graft copolymer obtained by copolymerizing a vinyl monomer having a glycidyl group and a crosslinking monomer. Patent Document 3 also discloses that the increase of the viscosity is prevented in the composition at with time, and the cured product has excellent impact resistance and adhesive strength. Patent Document 3 further discloses that the viscosity of the composition is increased by swelling of the graft part with the due to high affinity of the graft part with the matrix resin as a mechanism of increasing the viscosity of the composition after storage, and discloses a technology of improving the increase of the viscosity of the composition after storage by copolymerizing a crosslinking monomer with a graft part. However, in Patent Document 3, there is no suggestion that the viscosity of the composition is increased by the combination with given inorganic fillers. In addition, in Patent Document 3, there is no disclosure of the relation of the vinyl monomer having a glycidyl group on the graft part and the rate of increasing the viscosity of the composition. In addition, as indicated in Example of Patent Document 3, the impact resistance (sharpy impact strength) of the cured product is not necessarily improved compared with the impact strength of Comparative Example. Further, there is no descriptions of adhesive strength to impact and peel in Patent Document 3. Here, there is no correlation between dynamic peel strength such as adhesive strength to impact and peel and static peel strength such as T peel strength.